The present invention relates to radar systems and methods generally, and more specifically to digital beamforming techniques.
Conventional surveillance radar systems cannot resolve more than one target within a range-angle resolution cell while performing surveillance. Such resolution cells arise in radar from the use of finite signal bandwidth and antenna apertures.
In the case of an aircraft attack, it is possible for two or more vehicles to fly in close formation, so that a surveillance radar cannot resolve the number of targets until the aircraft are close to the radar, potentially losing valuable time in which defensive action might have been taken.
Similarly, in missile defense systems, it is possible for many targets within a single range-angle resolution cell to approach a surveillance radar without the radar being able to resolve the number of targets. In the missile defense scenario, the problem is compounded by the possibility that closely spaced re-entry vehicles, decoys, and/or debris may be present.
The failure to identify multiple threats within a single range cell can cause under-commitment of engagement measures.
The present invention is a method and system for identifying a number of targets within a main beam of an antenna array that transmits the main beam and receives echo returns from the main beam. A covariance matrix is generated using the echo returns. The presence of at least one target within a single range cell is detected. A plurality of consecutive pulses are transmitted in a direction of the single range cell within a sufficiently short period that the at least one target remains within the single range cell while the plurality of consecutive pulses are transmitted. An echo signal is sampled from each of the plurality of pulses. An updated covariance matrix is estimated each time the echo signal is sampled. An eigenvalue decomposition is updated each time the covariance matrix is updated. The number of targets in the single range cell is estimated, based on the eigenvalue decomposition.